The Universal Serial Bus (USB) is a connector standard that is in wide use. Currently, numerous standard bodies exist (USB 2.0) for enumerating requirements for implementation with USB connectors, including requirements for performance, hardware, form factor and various data transfer and connectivity protocols. As the USB connector becomes more popular and widespread, more applications and standards are adopted for the USB. In particular, there has been an effort to adopt standards by which the form factor of the USB becomes smaller, and has use in a variety of applications and environments in order to accommodate increasingly mobile and new computing devices.
As the name indicates, the USB connector acts as a data bus. In a standard mode of operation, the user is able to connect numerous devices to a single port using hubs. When devices are connected to a host, the host acts as a controller for all USB communications that enter through a particular port.
In general, the USB connector has a physical layer that includes hardware for implementing the data transfer protocol by which data is passed through the USB connector. The physical layer performs several functions, including serialization and de-serialization of transmissions, encoding and decoding of the signals. Across the USB connector, the protocol implemented provides for data packets that include token, data, and handshake packets.
Numerous standards have been and are currently being developed for the USB. These standards accommodate new smaller form factors, such as Mini or Micro-USB, as well as new data transfer protocols (e.g. USB 2.0). There is also a new standard for wireless USB ports. In addition, new standards accommodate use of USB connectors in various environments and applications. One standard is provided with “On-the-Go” which enables two devices connected through a USB port to negotiate for the role of the host. In particular, the On-The-Go Standard has introduced a Host Negotiation Protocol for enabling one device to act as host and controller in a one-to-one pairing.
Another more specific standard is the CEA-936A standard, which provides for use of USB connectors (Mini or Micro) in the context of “car kits”. In this context, a mobile computing device, or even a vehicle component, can utilize accessory devices such as stereo headsets and car chargers. Among other functionality, the CEA-936A standard provides for the host to have the ability to detect the particular type or kind of device connected to it, using signal line characteristics that are caused by the coupling of the particular device.